Because ellipsoidal heights gained either through GPS, which is widely used in our age, or through other means do not display the natural situation, they are far from meeting the practical precision needs concerning height. Orthometric heights received from the geoid up are more compatible with physical events and are accepted more natural and thus, with this very feature, they can be used successfully in solving many problems in practice related with height. Obtaining orthometric heights through traditional spirit leveling depends on weather conditions, is costly and requires too much labor and time. This is also the case for Turkey due to its topography being mountainous. In order to be able to convert h ellipsoidal heights which can be easily determined in GPS applications to H orthometric heights, N geoid heights are needed. Determining the best geoid model to be used in this transformation is important. In this article, OSU91A, EGM96, EIGENCG03C, GGM02S, GGM02C, EGM08 global geoid models and the Turkish Geoid – 2009 (TG-09), which is Turkish local gravimetric geoid, are compared with Turkish local GPS/Leveling geoid. In these comparisons, geoid heights at 30 points of Turkish National Fundamental GPS Network were used. In results of comparison, root mean square (RMS) of height differences between TG-09 model and GPS/Leveling geoid was 15 cm. It was observed that the global geoid that best fits GPS/Leveling geoid was EGM08. Root mean square (RMS) of height differences between EGM08 global model and GPS/Leveling geoid calculated was 87 cm.
Key words: Geoid, GPS/levelling, global geopotential model, Turkey.
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